Ancient Europeans lived alongside a half-ton bird nearly 12 feet tall

Inside a Crimean cave was a gigantic ancient mystery just waiting to be uncovered: a bird so large that it weighed nearly as much as an adult polar bear.

Thursday, June 27th 2019, 5:46 AM EDT

Andrey Atuchin via CNN

(CNN) -- Giant birds once roamed Madagascar, New Zealand and Australia. The latest fossil find, an intriguing fossilized femur, was recently found in Taurida Cave on the northern coast of the Black Sea.

It was discovered along with other fossils, including bison bones, that helped researchers date the now-extinct giant bird to between 1.5 million and 2 million years ago.

When the first early human ancestors arrived in Europe, they might have encountered these birds. The researchers think the bird probably reached the Black Sea region by crossing Turkey and the Southern Caucasus.

"When I first felt the weight of the bird whose thigh bone I was holding in my hand, I thought it must be a Malagasy elephant bird fossil because no birds of this size have ever been reported from Europe. However, the structure of the bone unexpectedly told a different story," study author Nikita Zelenkov of the Russian Academy of Sciences said in a statement.

This is the first time researchers have found a bird like this in Earth's Northern Hemisphereand the first time the size of the bird, named Pachystruthio dmanisensis, has been identified.

It probably stood 11½ feet tall and couldn't fly -- but this bird was fast. It was similar to elephant birds that went extinct in the 1700s, which were usually hindered by size when it came to speed, but the femur found as part of the fossil was long and slender, making for a better runner.

The femur is similar to that of the modern ostrich, which can reach a top speed of 43 miles per hour.

The researchers believe that speed was key to the bird's survival because its bones were found alongside those of giant cheetahs, hyenas and sabre-toothed cats. Some of these giant carnivores from the Ice Age were able to hunt mammoths.

"We don't have enough data yet to say whether it was most closely related to ostriches or to other birds, but we estimate it weighed about 450kg [992 pounds]," Zelenkov said. "This formidable weight is nearly double the largest moa, three times the largest living bird, the common ostrich, and nearly as much as an adult polar bear."

These birds likely lived off of fruit, making them herbivores.

Researchers were able to calculate the body mass of the bird based on measurements of the femur. A bird this huge probably evolved due to its environment. As the Last Ice Age approached, the environment grew more arid. A large body mass would be able to sustain itself on less nutritional food because of lower metabolic demands.

Similar fossils have been found at an archaeological site in Dmanisi, Georgia, which is known as the oldest human ancestor site outside Africa.

"The Taurida cave network was only discovered last summer when a new motorway was being built. Last year, mammoth remains were unearthed and there may be much more to that the site will teach us about Europe's distant past," Zelenkov said.